1. Field of the Invention
The present invention relates to the recovery of active catalyst from the process streams obtained from the hydrocyanation of olefins and the isomerization of certain nitriles and, more particularly, is directed to a process for separating zero-valent nickel catalyst from deactivated nickel catalyst prior to recycle of the active catalyst to the process.
2. Description of the Prior Art
Several patents disclose processes to which the present invention may be applied. One such process is an isomerization as disclosed in U.S. Pat. Nos. 3,853,948, issued on Dec. 10, 1974, and 3,536,748, issued on Oct. 27, 1970. Another process is disclosed in U.S. Pat. No. 3,496,215, issued on Feb. 17, 1970, and involves a process for the addition of one molecule of hydrogen cyanide to an olefin such as butadiene to produce a nonconjugated, ethylenically unsaturated organic nitrile, e.g., 3-pentenenitrile, 4-pentenenitrile (collectively referred to as 3,4-PN's), and 2-methyl-3-butenenitrile (2-M-3-BN). These patents do not disclose the use of promoters with the zero-valent nickel catalyst.
A method for the separation of organic phosphorus compounds and their metal complexes from organic nitriles in the hydrocyanation of olefins is disclosed in U.S. Pat. No. 3,773,809, issued on Nov. 20, 1973. The patentee discloses a process for separating organic phosphorus compounds and certain metal complexes from the hydrocyanation product fluid containing predominantly organic dinitriles and unreacted organic mononitriles by contacting the product with a cycloparaffin or paraffin hydrocarbon. The patentee teaches that his process is dependent upon the formation of a multi-liquid phase mixture upon contact with the hydrocarbon solvent. This multiphase mixture is assured by maintaining the molar ratio of organic mononitrile to organic dinitrile less than about 0.65 and preferably less than about 0.3. The patentee notes that in the multiphase mixture formed, organic phosphorus compounds and their zero-valent nickel complexes are found predominantly in the hydrocarbon solvent phase whereas organic mono- and dinitriles, catalyst promoter, catalyst promoter residue and degraded nickel catalyst are found predominantly in at least one other phase distinct from the hydrocarbon phase, (see Col. 3, lines 15-22 of the patent). The patentee further discloses that some of the degradation products of the hydrocyanation reaction as well as degraded nickel catalyst which may be at least partially in the form of nickel cyanide and nickel halide are soluble in the organic mononitriles and dinitriles while others are precipitated therefrom. In Example 6 the patentee discloses that the organic phosphorus compounds and nickel are predominantly found in the light (hydrocarbon) phase whereas the dinitriles, e.g., adiponitrile as well as the mononitriles, e.g., pentenenitriles, are found predominantly in the heavy dinitrile phase while degraded nickel catalyst tends to collect in the dinitrile phase as an insoluble residue. The patentees do not disclose at what point the catalyst solids are formed, if indeed, they are formed by the process disclosed. The patentee requires the formation of at least two liquid phases in the practice of his process.